The disclosed preferred embodiments in accordance with the present invention relate to an electronic code following relay that acts as a direct, or near direct, replacement for electro-mechanical relays used in railroad signaling systems.
Typically, these electro-mechanical relays are operated from either low nominal pulsed DC voltages of 1.7, or, by nominal pulsed DC voltages of 12. In railroad signaling applications, a code following relay is also known as being a code follower relay, or, a code responsive relay.
Railroad signaling systems have long incorporated in cab code signaled territories to transmit data to trains traveling along the tracks. This data is usually in the form of electrical pulses that are placed onto the rails. These pulses are then detected by the onboard electronic equipment located inside of the train's control cab, or locomotive, to display a cab signal to the train's engineer which assists in the safe movement of said train. A cab signal conveys to a train's driver, or engineer, advance information for the track conditions ahead of the train.
These coded pulses, typically may be, but not limited to, 100 Hz AC currents, or a combination of both 100 Hz and 250 Hz AC currents that are coded at, but not limited to, rates of 50, 75, 120, 180, 270, or 420 beats per minute which corresponds respectively to the frequencies of 0.833 Hz, 1.25 Hz, 2 Hz, 3 Hz, 4.5 Hz, and 7 Hz. Each code rate, with the exception of the 50 code rate, displays its own unique cab signal.
Typically, a Code Transmitter, or other railroad signaling system device, is responsible for the generation of the aforementioned code rates. The coded DC output currents of the Code Transmitter, or other railroad signaling system device, then drives the coil of electro-mechanical code following relays. The internal contacts of the electro-mechanical code following relay then makes/breaks 50 Hz, 60 Hz, 100 Hz, or 250 Hz AC currents, or a combination of any two (2) unlike frequency AC currents, to be placed onto the rails for the train's onboard cab signal system, and/or, other components of a railway signaling system to detect. Additionally, DC currents are also converted into a coded format for use by other components in a railroad signaling system.
If the coding currents are delivered out of specification onto the rails, said currents will be rejected by the train's onboard cab signal system, and, other components of a cab code railroad signaling system. This will result in the most restrictive cab signal to be displayed, and will cause unnecessary train delays. The same problems will arise if the coded currents are delivered onto the rails with inaccurate duty cycles. Duty cycle is understood to be the relationship of time, expressed in percentages, during a pulse, where 1/Freq.=Time (in seconds). An illustration is depicted in FIG. 7.
As shown in FIG. 7, each input code pulse has a duration of T which consists of an on-time period t1, and, an off-time period t2. One time cycle for any given frequency consists of an on-time period (t1), and, an off-time period (t2). The ratio of the on period t1 and the duration of T in percentage is the on-time, or, positive duty cycle portion of the pulse. The ratio of the off period t2 and the duration of T in percentage is the off-time duty cycle portion of the pulse. Ideally, t1 and t2 will be of equal durations forming what is commonly referred to as a 50/50 duty cycle. T is then understood to be equal to (t1+t2). Though other waveforms are available, the square waveform input pulse as presented in FIG. 7 is recommended for most cab code type railroad signaling systems. FIG. 6 illustrates the relationship of the coded AC currents of a dual frequency cab code signaling system that utilizes 100 Hz and 250 Hz frequencies. It should be noted that in a dual frequency AC signaling system, there are instances when the signaling system will utilize only one of two (2) AC frequencies to correspond to particular signal aspects. The 100 Hz and 250 Hz AC frequency currents should not be construed in a limiting sense, as one with skill in the art can readily contemplate that other AC frequencies could be used as well.
To meet the strict requirements relating to the correctness of the code rate and duty cycle, an appropriate code following relay is needed. Presently, railroads that operate with a cab code signaling system rely on expensive electro-mechanical code following relays to deliver the coded AC currents onto the rails. It has been observed that electro-mechanical code following relays can suffer with inaccurate output, and, have a high incidence of failure as well.
In electro-mechanical code following relays, steady AC currents are applied to a set of contacts. As the coil of said code following relay is coded, the internal contacts then code the applied AC steady current, or currents, at the same code rate that is applied to the relay's coil. However, when the relay contacts internally make and then break at the pre-determined code rate, electrical arcing can occur. This arcing action will, in time, cause the contact surfaces to become high resistive.
Highly resistive contacts will cause a failure in proper code rates being transmitted to the rails. Improper code rates, or, code rates applied at an insufficient power level, will cause unnecessary train delays.
A further important aspect for the coded currents is the duty cycle. Many electro-mechanical code following relays have been observed to produce inaccurate duty cycles. It has been observed that up to 15 milliseconds (0.015 seconds), or longer, can transpire before the opposing contacts are engaged once energy has been applied, or removed, to/from the electro-mechanical relay's coil.
This time delay is the result of the time that is required for the magnetic flux field of the relay's coil to reach a sufficient level to attract the armature, and, the time that transpires during the mechanical motion of the armature. The aforementioned conditions, and other factors, directly affect the on-time percentage (t1) of the code rate's duty cycle.
The off-time percentage of the code rate's duty cycle (t2) is usually dependent upon a spring that is connected to the electro-mechanical code following relay's armature to return the armature back to its original at rest state when controlling currents are removed from the relay's coil. Other factors that can influence the accuracy of the electro-mechanical code following relay include: return spring tension, spacing of the internal contacts, and, other mechanical factors.
Solid-state code following relays are therefore desirable to replace the existing electro-mechanical code following relays. Such solid-state code following relays can provide for coded DC output currents to satisfy other requirements in a railroad signaling system. Typically, in a high speed railroad signaling system, such as the GRS/Alstom AC voltage Phase Selective style, a code following relay can also output coded DC currents for the charging of resistor/capacitor networks, then, said electronic code following relay can also conduct the stored electrical potential from the resistor/capacitor networks to the coils of other DC controlled electro-mechanical relays in a railroad signaling system.
Other applications for a solid state code following relay would be to provide a DC power source to other DC controlled railroad signaling system relays, and, not be limited to the charging of resistor/capacitor networks. However, when a solid-state code following relay is used in conjunction with the charging of resistor/capacitor networks, to conduct the stored electrical potentials from the resistor/capacitor network(s) to the coils of other DC controlled electro-mechanical relay(s) in a railroad signaling system, the design can incorporate the use of solid-state relays having a low on-state voltage drop to ensure the resistor/capacitor networks receive the fullest charge potential from a DC power source.
Furthermore, the use of low on-state voltage drop solid-state relays in a railroad signaling system will also ensure the fullest potential electrical charge stored in resistor/capacitor networks will be transferred from the resistor/capacitor networks to the coil, or coils, of electro-mechanical relay(s) used in a railroad signaling system with minimal losses.
A solution for eliminating the problems associated with electro-mechanical code following relays is therefore to replace them with an electronic version that will function in the same capacity as either a direct, or near direct, replacement device. An electronic replacement version for the electro-mechanical code following relay is desired to also exhibit the same break before make (Form C) Single Pole-Double Throw (SPDT) type operations for one or more sets of contacts.
Furthermore, an electronic version of the electro-mechanical code following relay is desirably made compatible with a railroad's present signaling system, as well as to meet the future needs for a cab code system that will employ the coding of two (2), or more, unlike frequency AC currents.
Furthermore, an electronic code following relay is desirable to also satisfy the need for a window, or time break, to be present between the transmission of two (2) unlike frequency AC currents as prescribed by the specifications of a dual frequency type cab code railroad signaling system.